May 30, 2015
Extraction is a separation technique frequently used to isolate one or more substances (solid, liquid, or both) from a mixture. Solvent extraction is based on the principle of the equilibrium distribution of a solute between two immiscible phases, which causes partitioning between aqueous and organic layers, one of which is a solvent. The desired substance is dissolved in the solvent; the solvent is then evaporated leaving behind only the desired substance. However, the substance extracted is not pure, crystallization or distillation will need to be performed to purify the substance after extraction.
A 0.110g aliquot of benzoic acid was placed in in 5.0mL conical vial fitted with a screw cap. using a graduated cylinder 2.0mL of water were added to the benzoic acid, followed by 2.0mL of methylene chloride. The screw cap was placed on the conical vial and the mixture was shaken until the benzoic acid was completely dissolved, approximately 30 - 45 seconds. The conical vial was placed upright on the counter for 5 minutes to allow the organic and aqueous layers to separate. While allowing the layers in the first conical vial to separate, a second 5.0mL conical vial was filled with 0.200g of anhydrous, granular sodium sulfate, a drying agent. After allowing the organic (which in this case is the bottom layer) and aqueous (top) layers to separate, the entire organic layer, or methylene chloride solution, of the first vial was drawn into a Pasteur pipette and transferred to the vial containing the drying agent. The vial was capped and allowed to sit undisturbed for 5 minutes to allowing drying. While waiting for the drying agent to soak up any remnants of the aqueous layer a third conical vial was obtained. A boiling stone was placed in the vial and the vial was tarred. After waiting 5 minutes the methylene chloride solution was primarily clear with a few small, cloudy bubbles on top of the solution which were remnants of the aqueous layer from the first conical vial. The clear methylene chloride solution was transferred to the tarred conical vial containing a boiling stone using a Pasteur pipette being careful not to transfer the cloudy bubbles of aqueous layer. The sodium sulfate which was left in the bottom of the second conical vial was rinsed with 1.0mL of methylene chloride and the rinse added to the conical vial containing the boiling stone. The vial containing the boiling stone and methylene chloride solution was placed on on a hot plate under the fume hood. The heat was adjusted so that the methylene chloride solution remained at a steady boil and the solvent was allowed to evaporate. Once all solvent was evaporated and only benzoic acid crystals and the boiling stone were left in the vial, the vial was tarred again using the same scale that was used to tare the vial and boiling stone alone.
Vial w/ Boiling Stone
Vial w/ Boiling Stone & Extracted Benzoic Acid
Extracted Benzoic Acid
(Methylene Chloride layer)
Kp = (0.167)/(0.110) = -2.93
Recovery % = (weight of compound recovered)/(weight of original sample) * 100
Recovery % = (0.167g/0.110g) *100
Recovery % = 152%
According to the calculations more benzoic acid was recovered than was originally obtained to perform this experiment. Since benzoic acid was only moved between phases and different solvents and not created during the extraction, errors must have been made to result in this data. One factor that could cause erroneous results…